Magnetorheological fluid compositions and prosthetic knees utilizing same

ABSTRACT

The present invention relates in one embodiment to magnetorheological fluids utilized in prosthetic joints in general and, in particular, to magnetorheological fluids utilized in controllable braking systems for prosthetic knee joints. Preferred magnetorheological fluids of the present invention comprises polarizable iron particles, a carrier fluid, and optionally an additive. Preferred additives include, but are not limited to functionalized carrier fluids as well as derivatized fluoropolymers. Preferred carrier fluids include, but are not limited, to perfluorinated polyethers.

RELATED APPLICATION DATA

This application is a continuation application of U.S. patentapplication Ser. No. 10/722,313 filed Nov. 25, 2003 which claimspriority under 35 U.S.C. 119(e) from provisional application Ser. No.60/467,722 filed May 2, 2003, the entirety of which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in one embodiment to magnetorheologicalfluids utilized in prosthetic joints in general and, in particular, tomagnetorheological fluids utilized in controllable braking systems forprosthetic knee joints.

2. Description of the Related Art

Three types of variable-torque brakes have been employed in prostheticknees in the past: (i) dry friction brakes where one material surfacerubs against another surface with variable force; (ii) viscous torquebrakes using hydraulic fluid squeezed through a variable sized orificeor flow restriction plate; and (iii) magnetorheological (MR) brakes ordampers where MR fluid (containing small iron particles suspended in thefluid) is squeezed through a fixed orifice or flow restriction plate,with viscosity of the fluid being varied in response to an appliedmagnetic field. Each of these technologies, as conventionally practicedin the field of prosthetics, can pose certain disadvantages.

Though dry friction brakes can generally provide a substantial torquerange for their size, undesirably, they are often difficult to control.After extended use, the frictional pads tend to wear, thereby changingthe frictional characteristics of the brake and the torque response fora given commanded torque. Disadvantageously, this can cause unreliabledamping performance, and hence adversely affect the gait of the amputeeand also cause discomfort to the amputee. Consequently, dry frictionbrakes may need frequent servicing and/or replacement which undesirablyadds to the cost.

Under high loading conditions, viscous torque brakes are susceptible toleakage of hydraulic fluid and possibly other damage due to excessivepressure build-up. Disadvantageously, this can result in an irreversiblestate, since once the brake unit is overloaded it cannot return tonormal. Therefore, such a viscous torque brake for a prosthetic joint isprone to catastrophic failure, and hence can be unreliable anddetrimental to the safety of an amputee.

In certain MR brakes and dampers, the interaction of the MR fluid withthe device causes increased pressure, seal deterioration, or acombination of the two. Another possible cause of these adverse effectsis decomposition of the MR fluid. Once the seals fail or the MR fluiddecomposes, the prosthetic knee is no longer suitable for use.

SUMMARY OF THE INVENTION

In accordance with preferred embodiments, there is provided amagnetorheological fluid (MR fluid) comprising polarizable particles, acarrier fluid, and optionally an additive. In one embodiment, thepolarizable particles comprise iron particles ranging in size from about0.1 to about 100 microns, preferably from about 0.2 to about 50 microns,from about 0.4 to about 10 microns, or from about 0.5 to about 9microns, but also including about 0.3, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4,5, 6, 7, 8, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 40, 60, 70,80, and 90 microns, and ranges encompassing such sizes. In certainembodiments, iron particles comprise from about 1 to about 60% (v/v) ofthe total MR fluid volume, preferably from about 10 to about 50% (v/v),from about 20 to about 40% (v/v), but also including about 5, 15, 25,30, 35, 45, and 55% (v/v) and ranges encompassing such percentages.

Suitable candidates for carrier fluids include, but are not limited to,silicone, hydrocarbon, esters, ethers, fluorinated esters, fluorinatedethers, mineral oil, unsaturated hydrocarbons, and water based fluids.In one embodiment, a preferred carrier fluid comprises an aliphatichydrocarbon. In another embodiment, a preferred carrier fluid comprisesa perfluorinated polyether (“PFPE”).

In one embodiment, a preferred additive comprises a functionalizedfluoropolymer, including, but not limited to, a parafluoropropene andoxygen polymerized amide derivative. In another embodiment, a preferredadditive comprises a functionalized carrier fluid. Suitable candidatesfor monofunctionalized PFPE carrier fluid derivatives include, but arenot limited to silane, phosphate, hydroxyl, carboxylic acid, alcohol andamine functions. Suitable candidates for difunctional PFPE carrier fluidderivatives include, but are not limited to, dihydroxyl, ethoxy ether,isocyanate, aromatic, ester and alcohol functions. In one embodiment, apreferred functionalized PFPE carrier fluid comprises apoly(hexafluoropropylene epoxide) with a carboxylic acid located on theterminal fluoromethylene group. In one embodiment, the additivecomprises from about 0.1 to about 20% (v/v) of the carrier fluid,preferably from about 1 to about 15% (v/v), or from about 2 to about 10%(v/v), but also including about 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7,7.5, 8, 8.5, 9, 9.5, 11, 12, 13, 14, 16, 17, 18, and 19% (v/v) andranges encompassing such percentages.

In one embodiment, a preferred MR fluid comprises about 28% (v/v)particles, and about 72% (v/v) fluid component wherein said fluidcomponent comprises about 5% (v/v) poly(hexafluoropropylene epoxide)with a carboxylic acid located on the terminal fluoromethylene groupadditive and about 95% (v/v) PFPE oil carrier fluid. In anotherembodiment, a preferred MR fluid comprises about 32% (v/v) particles,and about 68% (v/v) fluid component wherein said fluid componentcomprises about 5% (v/v) poly(hexafluoropropylene epoxide) with acarboxylic acid located on the terminal fluoromethylene group additiveand about 95% (v/v) PFPE oil carrier fluid. In another embodiment, apreferred MR fluid comprises about 28% (v/v) particles and about 72%(v/v) fluid component wherein said fluid component comprises about 5%(v/v) parafluoropropene and oxygen polymerized amide derivative additiveand about 95% (v/v) PFPE oil carrier fluid. In another embodiment, apreferred MR fluid comprises about 32% (v/v) particles and about 68%(v/v) fluid component wherein said fluid component comprises about 5%(v/v) parafluoropropene and oxygen polymerized amide derivative additiveand about 95% (v/v) PFPE oil carrier fluid. In embodiments containingPFPE oil, the PFPE oil may comprise substantially all one PFPE oil or amixture of one or more PFPE oils.

In one embodiment, an MR fluid is specifically designed for use in ashear mode device. For such a device, mechanically hard particles aredesired. The carrier fluid also desirably experiences a less dramaticviscosity change over temperature changes as compared to other fluids.This may be measured in terms of a viscosity index (test method ASTMD-2270) with preferred carrier fluids having higher viscosity indices.In one embodiment, preferred carrier fluids have viscosity indicespreferably ranging from about 100 to about 340 based on kinematicviscosity at 104 and 212° F., from about 120 to about 320, from about140 to about 300, but also including 160, 180, 200, 220, 240, 255, 260,280, and ranges encompassing these amounts. One embodiment thataccomplishes this includes a carrier fluid comprising one or more PFPEoils. For example, a preferred PFPE fluid, UNIFLOR™ 8510 has a viscosityindex of 255. Without wishing to be bound by any theory, it is believedthat preferred PFPE oils of certain embodiments demonstrate desirableviscosity indices due to their narrow distribution of molecular weights.Also, the MR fluid desirably does not produce a significant amount ofvapor in a sealed chamber so as to interfere with the function of thedevice. In one embodiment, a fluid component comprising PFPE oil carrierfluid and a functionalized fluoropolymer additive provides thisproperty. Without wishing to be bound by any theory, it is believed thatpreferred PFPE oils of certain embodiments are less volatile, i.e. lowervapor pressures than other oils, because they have much higher molecularweights, e.g. about 2,000 to about 15,000, and therefore do not producea significant amount of vapor.

In addition, a shear mode device should provide sufficient torque, forexample torque production in one embodiment may be about 0.1 to about200 Newton-meters, more preferably about 0.3 to about 150 Newton-meters,even more preferably about 0.5 to about 100 Newton-meters, but alsoincluding about 0.8, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, and75 Newton-meters. In one embodiment, maintaining a sufficient ratio ofparticles, such as iron particles, to MR fluid provides for this. In oneembodiment, a suitable ratio is achieved when the iron particlescomprise from about 1 to about 60% (v/v) of the total MR fluid volume,preferably from about 10 to about 50% (v/v), more preferably from about20 to about 40% (v/v), but also including about 5, 15, 25, 30, 35, 45,and 55% (v/v) and ranges encompassing these percentages.

In accordance with preferred embodiments, there is provided a MR fluidcomprising polarizable particles, a carrier fluid, and optionally anadditive for use in a prosthetic knee, for example, a knee as describedin U.S. Patent Publication 2001/0029400A1. In one embodiment, theprosthetic knee comprises at least two adjacent surfaces adapted forshear movement relative to one another wherein the MR fluid is containedbetween said adjacent surfaces. In one embodiment, the MR fluid used incombination with the knee comprises PFPE oil carrier fluid andparticles, such as polarizable particles described above. In oneembodiment, the polarizable particles comprise iron particles ranging insize from about 0.1 to about 100 microns, preferably from about 0.2 toabout 50 microns, more preferably from about 0.4 to about 10 microns,even more preferably from about 0.5 to about 9 microns, but alsoincluding about 0.3, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 11, 12,13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 40, 60, 70, 80, and 90 microns,and ranges encompassing these sizes. In certain embodiments, ironparticles comprise from about 1 to about 60% (v/v) of the total MR fluidvolume, preferably from about 10 to about 50% (v/v), more preferablyfrom about 20 to about 40% (v/v), but also including about 5, 15, 25,30, 35, 45, and 55% (v/v) and ranges encompassing such percentages.

In another embodiment, the MR fluid used in combination with aprosthetic knee optionally includes an additive. In one embodiment, apreferred additive comprises a functionalized fluoropolymer, morepreferably a parafluoropropene and oxygen polymerized amide derivative.In another embodiment, a preferred additive comprises a functionalizedcarrier fluid. Suitable candidates for monofunctionalized PFPE carrierfluid derivatives include, but are not limited to silane, phosphate,hydroxyl, carboxylic acid, alcohol and amine functions. Suitablecandidates for difunctional PFPE carrier fluid derivatives include, butare not limited to, dihydroxyl, ethoxy ether, isocyanate, aromatic,ester and alcohol functions. In one embodiment, a preferredfunctionalized PFPE oil comprises a poly(hexafluoropropylene epoxide)with a carboxylic acid located on the terminal fluoromethylene group. Inone embodiment, the additive comprises from about 0.1 to about 20% (v/v)of the carrier fluid, preferably from about 1 to about 15% (v/v), morepreferably from about 2 to about 10% (v/v), but also including about2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 11, 12, 13,14, 16, 17, 18, and 19% (v/v), and ranges encompassing these amounts.

In another embodiment, the passage or cavity of the knee that holds theMR fluid contains a volume of about 1 to about 10 ml, preferably fromabout 2 to about 9 ml, more preferably from about 3 to about 8 ml, butalso including about 4, 5, 6, and 7 ml, and ranges encompassing thesevolumes. In one embodiment, the MR fluid fills the cavity to about 70%of its capacity, but ranges from about 50 to about 100% as well about55, 60, 65, 75, 80, 85, 90 and 90% and ranges encompassing these amountsare also acceptable.

In another embodiment, the MR fluid used in combination with aprosthetic knee in shear mode in one embodiment utilizes a MR fluid thatis operable over a temperature range from about 10 to about 115° F., butalso including about 20, 30, 40, 50, 60, 70, 80, 90, 100, and 110° F.Operability in one embodiment depends on viscosity, wherein the carrierfluid desirably has a viscosity at 104° F. of about 10 to about 100 cSt(centistokes), more preferably about 30 to about 80 cSt, even morepreferably about 50 to about 70 cSt, but also including about 10, 20,25, 35, 40, 45, 55, 60, 65, 75, 85, 90, and 95 cSt.

Desirably, operation of a prosthetic knee in shear mode in oneembodiment preferably utilizes a carrier fluid with a pour pointpreferably ranging from about −70° C. to about 40° C., from about −65°C. to about −45° C., but also including about −50° C., −55° C., and −60°C., and ranges encompassing these temperatures. In another embodiment,operation of a prosthetic knee in shear mode preferably utilizes acarrier fluid with a percent volatility at 121° C. preferably rangingfrom about 0.01% to about 20%, from about 0.02% to about 15%, from 0.03%to about 12%, but also including about 0.05%, 0.08%, 0.1%, 0.2%, 0.3%,0.4%, 0.5%, 0.7%, 0.9%, 1%, 3%, 5%, 7%, 9%, 17%, and ranges encompassingthese percentages.

In one embodiment, a preferred MR fluid used in combination with aprosthetic knee in shear mode comprises about 28% (v/v) particles, andabout 72% (v/v) fluid component wherein said fluid component comprisesabout 5% (v/v) poly(hexafluoropropylene epoxide) with a carboxylic acidlocated on the terminal fluoromethylene group additive and about 95%(v/v) PFPE oil carrier fluid. In another embodiment, a preferred MRfluid used in combination with a prosthetic knee in shear mode comprisesabout 32% (v/v) particles, and about 68% (v/v) fluid component whereinsaid fluid component comprises about 5% (v/v) poly(hexafluoropropyleneepoxide) with a carboxylic acid located on the terminal fluoromethylenegroup additive and about 95% (v/v) PFPE oil carrier fluid. In anotherembodiment, a preferred MR fluid used in combination with a prostheticknee in shear mode comprises about 28% (v/v) particles, and about 72%(v/v) fluid component wherein said fluid component comprises about 5%(v/v) parafluoropropene and oxygen polymerized amide derivative additiveand about 95% (v/v) PFPE oil carrier fluid. In another embodiment, apreferred MR fluid comprises about 32% (v/v) particles and about 68%(v/v) fluid component wherein said fluid component comprises about 5%(v/v) parafluoropropene and oxygen polymerized amide derivative additiveand about 95% (v/v) PFPE oil carrier fluid. In embodiments containingPFPE oil, the PFPE oil may comprise substantially all one PFPE oil or amixture of one or more PFPE oils.

All of these embodiments are intended to be within the scope of theinvention herein disclosed. These and other embodiments of the presentinvention will become readily apparent to those skilled in the art fromthe following detailed description of the preferred embodiments havingreference to the attached figures, the invention not being limited toany particular preferred embodiment(s) disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 depict one embodiment of a prosthetic knee suitable foruse in preferred embodiments. FIGS. 1 and 2 correspond to FIGS. 4 and 5,respectively, of U.S. patent Publication 2001/0029400A1 (applicationSer. No. 09/767,367), filed Jan. 22, 2001, entitled “ELECTRONICALLYCONTROLLED PROSTHETIC KNEE,” the entire disclosure of which is herebyincorporated by reference herein. More specifically, the description ofthe drawings and the item numbers depicted in the drawings are describedin detail in the above referenced patent publication. FIG. 1 is adetailed exploded perspective view of a magnetorheologically actuatedprosthetic knee having features and advantages in accordance with onepreferred embodiment of the present invention. FIG. 2 is a cross sectionview of the prosthetic knee of FIG. 1.

FIGS. 3-5 illustrate dynamic viscosity curves for various carrier oilsand MR fluid samples.

FIG. 6 illustrates a comparison of the viscosities of various carrieroils and MR fluids.

FIG. 7 is a front view of one of the core side plates of FIG. 1 havingfeatures and advantages in accordance with one preferred embodiment ofthe present invention.

FIG. 8 is a rear view of the core side plate of FIG. 7.

FIG. 9 is a cross section view along line 11-11 of FIG. 7.

FIG. 10 is an end view of the inner spline of FIG. 1 having features andadvantages in accordance with one preferred embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Disclosed herein are magnetorheological fluids (MR fluids) suitable foruse in magnetorheological knee brakes or actuators. More particularly,the disclosed MR fluids may be applicable to prosthetic knee jointswhich operate in shear mode, for example, where the MR fluid is providedbetween adjacent surfaces, such as between parallel plates or in theannular space between inner and outer cylinders. Certain embodiments ofa magnetorheological knee brake or actuator that may employ the MRfluids as described herein are described in U.S. Patent Publication2001/0029400A1 (application Ser. No. 09/767,367), filed Jan. 22, 2001,entitled “ELECTRONICALLY CONTROLLED PROSTHETIC KNEE,” the entiredisclosure of which is hereby incorporated by reference herein. FIGS. 1and 2, corresponding to FIGS. 4 and 5 of U.S. Patent Publication2001/0029400A1, also depict one embodiment of a magnetorheological kneebrake or actuator that may employ the MR fluids as described herein.Certain embodiments of a control scheme and system formagnetorheological knee brakes or actuators are described in copendingU.S. Patent Publication 2002/0052663A1 (application Ser. No.09/823,931), filed Mar. 29, 2001, entitled “SPEED-ADAPTIVE ANDPATIENT-ADAPTIVE PROSTHETIC KNEE,” the entire disclosure of which ishereby incorporated by reference herein. It will be appreciated,however, that the MR fluids as described herein may have applicabilityto other devices which utilize MR fluids, including but not limited to,other devices operating in a shear mode.

In one embodiment, the magnetorheological fluid preferably comprises aplurality of iron, ferrous or magnetic particles suspended in fluid.These suspended particles form torque producing chains in response to anapplied magnetic field. Thus, the magnetorheological (MR) fluidundergoes a rheology or viscosity change or variation, which isdependent on the magnitude of the applied magnetic field. In turn, thisvariation in the bulk fluid viscosity determines the magnitude of theshearing force/stress or torque generated, and hence the level ofdamping or braking provided by the prosthetic knee or other device.Typically, the bulk viscosity of the MR fluid increases with increasingstrength of the applied field. By controlling the magnitude of thismagnetic field, the rotary motion of an artificial limb is rapidly andprecisely adjusted and/or controlled, for example, to control theflexion and extension during swing and stance phases to provide a morenatural and safe ambulation for the amputee. Preferably the MR fluid hasone or more of the following properties: a high magnetic flux capacityand low magnetic remanence and low viscosity while having a largemagnetic field induced shearing stress so that, advantageously, aprosthetic knee in one embodiment, provides a wide dynamic torque range.

In one embodiment, the MR fluid preferably comprises a carrier fluidwith polarizable ferrous or iron particles. As used herein, the termcarrier fluid is a broad term used in its ordinary sense and includesembodiments wherein the specific carrier fluids described below are theprimary component and embodiments wherein the carrier fluid comprisesthese specific fluids as well as additives described below. In addition,embodiments wherein the additives described below are the primarycarrier fluid are also contemplated. In one embodiment, such as whenused between rotor-stator surfaces of US 2001/0029400A1, these particleshave a size on the order of a micron or a few microns. Ideally the MRfluid exhibits shear rate thinning behavior where MR fluid viscositydecreases with increasing shear rate. This advantageously minimizes theviscous torque due to shearing of the MR fluid between each rotor-statorpair under zero-field conditions (that is, when the electromagnet is notenergized), and hence allows for a larger operating torque range.Further, in one embodiment MR fluids used in combination with aprosthetic knee desirably exhibit low off-state viscosity and thereforelow off-state torque as torque is proportional to MR fluid viscosity.The viscosity of preferred MR fluids in certain embodiments may bealtered by one or more of the following: increasing or decreasing theparticle loading, including an additive, changing the carrier fluid, ormixing two or more carrier fluids.

Suitable candidates for carrier fluids include, but are not limited to,silicone, hydrocarbon, esters, ethers, fluorinated esters, fluorinatedethers, mineral oil unsaturated hydrocarbons, and water based fluids. Inone embodiment, the carrier fluid comprises substantially all one fluid.In another embodiment, the carrier fluid is a mixture of one or morecarrier fluids. In one embodiment, the carrier fluid preferablycomprises an aliphatic hydrocarbon. In another embodiment the carrierfluid preferably comprises a perfluorinated polyether (PFPE), also knownas perfluoropolyether, perfluoroalkylether or perfluoropolyalkylether,fluid. In certain embodiments, a preferred PFPE oil comprises fluorineend capped branched homopolymers of hexafluoropropylene epoxide with thefollowing chemical structure:

Where n=10-60

In another embodiment, a preferred PFPE oil comprises a branched PFPEcontaining pendent trifluoromethyl groups, (—CF₃), with the followingstructure:CF₃CF₂CF₂O—[CF(CF₃)CF₂—O—]_(n)CF₂CF₃

Where n=5-65

In another embodiment, a preferred PFPE oil comprises a linear PFPE withthe following structure:CF₃O—[CF₂CF₂—O—]_(z)[CF₂—O—]_(p)CF₃Where the ratio of z:p is between about 0.5:1 and 2:1, and z+p isbetween about 40 and about 180. In another embodiment, a preferred PFPEoil comprises a linear PFPE with the following structure:CF₃CF₂CF₂O—[CF₂CF₂CF₂—O—]_(n)CF₂CF₃

Where n=10-50

In another embodiment, a preferred PFPE oil comprisesperfluoropropylpolyether. As presently contemplated preferredperfluorinated polyethers may be purchased from Nye Lubricants(Fairhaven, Mass., USA) and include, but are not limited to, UNIFLOR™8510, UNIFLOR™ 8130, UNIFLOR™ 8140, UNIFLOR™ 8730 and UNIFLOR™ 8970.Suitable perfluorinated polyethers may also be purchased from E.I. duPont de Nemours and Company, (Wilmington, Del., USA) and include, butare not limited to, Krytox® GPL-103, Krytox® L-65 oil, Krytox® XP 1A4oil, Krytox® L-100, Krytox® 1525, Krytox® 1525S, and Krytox® 1531.

Other ingredients can be optionally added to the carrier fluids ofpreferred embodiments to enhance the performance properties of preferredcarrier fluids. In some embodiments, preferred additives include, butare not limited to, functionalized carrier fluids. In embodimentscomprising perfluorinated polyethers, desirable additives can alsoinclude, but are not limited to, functionalized PFPE oils as well asderivatized fluoropolymers. Suitable candidates for monofunctionalizedPFPE derivatives include, but are not limited to silane, phosphate,hydroxyl, carboxylic acid, alcohol and amine functions. Suitablecandidates for difunctional PFPE derivatives include, but are notlimited to, dihydroxyl, ethoxy ether, isocyanate, aromatic, ester andalcohol functions. In some embodiments, functionalized perfluorinatedpolyether fluid additive comprises one or more functional groupsselected from the group consisting of silane, phosphate, hydroxyl,carboxylic acid, amine, dihydroxyl, ethoxy ether, isocyanate, aromatic,ester and alcohol functions. More specifically, in one embodimentcomprising perfluorinated polyethers, a preferred functionalized PFPEoil comprises a poly(hexafluoropropylene epoxide) with a carboxylic acidlocated on the terminal fluoromethylene group. As presently contemplatedpreferred functionalized PFPE oils are Krytox (157 FSL and Krytox® 157FSM available from E.I. du Pont de Nemours and Company, (Wilmington,Del., USA). In another embodiment, a preferred fluoropolymer comprises aparafluoropropene and oxygen polymerized amide derivative. As presentlycontemplated a preferred parafluoropropene and oxygen polymerized amidederivative additive is FOMBLIN DA 306 available from Solvay Solexis(Thorofare, N.J., USA).

Suitable candidates for polarizable ferrous or iron particles include,but are not limited to, particles ranging in size from about 0.1 toabout 100 microns, preferably from about 0.2 to about 50 microns, morepreferably from about 0.4 to about 10 microns, even more preferably fromabout 0.5 to about 9 microns, but also including about 0.3, 0.6, 0.7,0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 11, 12, 13, 14, 15, 16, 17, 18, 19,20, 25, 30, 40, 60, 70, 80, and 90 microns, and ranges encompassingthese sizes. In certain embodiments, preferred particles aremechanically hard. As presently contemplated preferred iron particlesare available from BASF AG (Ludwigshafen, Germany) and include, but arenot limited to, BASF Carbonyl Iron Powder OM, BASF Carbonyl Iron PowderHQ, BASF Carbonyl Iron Powder HS, BASF Carbonyl Iron Powder EW, BASFCarbonyl Iron Powder HS-I, and BASF Carbonyl Iron Powder HL-I. Othersuitable iron particles may also be purchased from ISP Corporation(Wayne, N.J., USA). Other suitable ferrous or iron particles well knownto those of skill in the art may also be used. In related embodiments,particles comprising magnetic or ferromagnetic materials other than ironmay be used alone or in combination with iron-based particles.

In accordance with a preferred embodiment, the MR fluid compositioncomprises polarizable iron particles, PFPE carrier fluid, and anadditive. In one embodiment, the iron particles comprise from about 1 toabout 60% (v/v) of the total MR fluid volume, preferably from about 10to about 50% (v/v), more preferably from about 20 to about 40% (v/v),but also including about 5, 15, 25, 30, 35, 45, and 55% (v/v) and rangesencompassing such percentages. To determine the weight of particlesrequired to achieve the proper % (v/v), the required volume ismultiplied by the density of the particles. In one embodiment, theadditive comprises from about 0.1 to about 20% (v/v) of the carrierfluid, preferably from about 1 to about 15% (v/v), more preferably fromabout 2 to about 10% (v/v), but also including about 2.5, 3, 3.5, 4,4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 11, 12, 13, 14, 16, 17, 18,and 19% (v/v) and ranges encompassing such percentages. For example, inone embodiment a preferred MR fluid comprises about 28% (v/v) ironparticles and about 72% (v/v) fluid component wherein said fluidcomponent comprises about 5% (v/v) a parafluoropropene and oxygenpolymerized amide derivative additive and about 95% (v/v) PFPE carrierfluid. In another embodiment, a preferred MR fluid comprises about 32%(v/v) particles and about 68% (v/v) fluid component wherein said fluidcomponent comprises about 5% (v/v) parafluoropropene and oxygenpolymerized amide derivative additive and about 95% (v/v) PFPE oilcarrier fluid. In another embodiment, a preferred MR fluid comprisesabout 28% (v/v) particles, and about 72% (v/v) fluid component whereinsaid fluid component comprises about 5% (v/v) poly(hexafluoropropyleneepoxide) with a carboxylic acid located on the terminal fluoromethylenegroup additive and about 95% (v/v) PFPE oil carrier fluid. In anotherembodiment, a preferred MR fluid comprises about 32% (v/v) particles,and about 68% (v/v) fluid component wherein said fluid componentcomprises about 5% (v/v) poly(hexafluoropropylene epoxide) with acarboxylic acid located on the terminal fluoromethylene group additiveand about 95% (v/v) PFPE oil carrier fluid. In embodiments containingPFPE oil, the PFPE oil may comprise substantially all one PFPE oil or amixture of one or more PFPE oils.

The MR fluid ingredients may be combined in any order and mixed by anysuitable means including, but not limited to, stirring, agitation,sonification or blending. In accordance with a preferred embodiment,additives are first mixed with carrier fluids and stirred. Carrier fluidis added to the iron particles and the ingredients are stirred. Theparticles are then dispersed using sonification. The resulting MR fluidis then heated. A detailed example is provided below in the examplesection.

When the MR fluids as described herein are used in combination with aprosthetic knee, for example, a knee as described in U.S. patentPublication No. 2001/0029400A1, certain characteristics of the fluid aswell as the knee may be desired. In one embodiment, such as shown inFIGS. 4 and 5 of U.S. 2001/0029400A1 and FIGS. 1 and 2 disclosed hereinand described in further detail below, a knee may contain a cavity orpassage for holding MR fluid between a plurality of rotors and stators.The number of rotors and stators in certain embodiments may be increasedor reduced in order to alter the off-state or low-end torque propertiesof the MR fluid used in combination with the knee. In one embodiment,the number of rotors and stators preferably range from about 50 to about90, preferably from about 55 to about 70, but also including about 57,59, 61, 63, 65, 67, and ranges encompassing these amounts. The kneecavity may contain a volume of about 1 to about 10 ml, preferably fromabout 2 to about 9 ml, more preferably from about 3 to about 8 ml, butalso including about 4, 5, 6, and 7 ml. In one embodiment, the MR fluidfills the cavity to about 70% of its total volume, but may range fromabout 50 to about 100% as well about 55, 60, 65, 75, 80, 85, 90 and 90%.The MR fluid advantageously demonstrates one or more of the following:relatively low volatility, stable viscosity, thermal stability, and astable composition. In addition, in certain embodiments it is desirablethat the cavity or passage containing the MR fluid does not exhibitundesirable pressure levels. Without wishing to be bound by any theory,it is believed that an unsuitable fluid may release gases or volatilizecausing pressure within the prosthetic knee to increase to anundesirable level. If the pressure is too high, the integrity of theprosthetic knee seals can be compromised. In certain embodiments it isdesirable that a prosthetic knee utilizing a MR fluid produces torque ofabout 0.1 to about 200 Newton-meters, more preferably about. 0.3 toabout 150 Newton-meters, even more preferably about 0.5 to about 100Newton-meters, but also including about 0.8, 1, 2, 3, 4, 5, 6, 7, 8, 9,10, 20, 30, 40, 50, and 75 Newton-meters.

FIGS. 1 and 2 show a controllable rotary prosthetic knee joint 210having features and advantages in accordance with one preferredembodiment of the present invention. The prosthetic knee 210 generatescontrollable dissipative forces preferably substantially along or aboutthe knee axis of rotation 224.

The electronically controlled knee 210 generally comprises a generallycentral core 212 in mechanical communication with a pair of rotatableside plates 216, 218, an electromagnet 214, a plurality of blades orrotors 220 in mechanical communication with a rotatable inner spline222, a plurality of blades or stators 230 in mechanical communicationwith a rotatable outer spline 232, a pair of ball bearings 226, 228 fortransferring rotary motion to a pair of outer side walls or forks 236,238. The rotation is substantially about the knee axis of rotation 224.

The plurality of rotors 220 and stators 230 are preferably interspersedin an alternating fashion and the gaps or microgaps between adjacentblades 220 and 230 comprise thin lubricating films of amagnetorheological (MR) fluid, which thereby resides in the cavity orpassage formed between the inner spline 222 and the outer spline 232.This preferred embodiment provides a controllable and reliableartificial knee joint, which advantageously has a wide dynamic torquerange, by shearing the MR fluid in the multiple gaps or flux interfacesbetween adjacent rotors 220 and stators 230.

Preferably, end-threaded rods 248 and nuts 250 are used to secureselected components of the prosthetic knee 210, thereby allowing astraightforward assembly and disassembly procedure with a minimum offasteners. Alternatively, or in addition, various other types offasteners, for example, screws, pins, locks, clamps and the like, may beefficaciously utilized, as required or desired, giving due considerationto the goals of providing secure attachment, and/or of achieving one ormore of the benefits and advantages as taught or suggested herein.

Preferably, the core 212 and associated side plates 216, 218 are formedof a magnetically soft material of high flux saturation density and highmagnetic permeability. Thus, when the electromagnet 214 is actuated amagnetic field, circuit or path is generated or created within the kneejoint 210. In one preferred embodiment, the magnetic field passeslongitudinally (parallel to the axis of rotation 224) through thecentral core 212, radially through the side plate 218, laterally(parallel to lateral direction 242) through the interspersed set ofrotors 220 and stators 230 and the magnetorheological (MR) fluid, andradially through the side plate 216. The orientation or positioning ofthe electromagnet 214 and the direction of current flow through itdetermines the polarity of the magnetic field, and thereby determineswhether the magnetic field passes radially inwards or outwards throughthe side plate 218, and hence in the correspondingly opposite directionthrough the side plate 216. The portion of the magnetic field passingthrough the core 212 and side plates 216, 218 generally defines themagnetic return path while the active or functional magnetic field isgenerally defined by the magnetic path through the rotors 220, stators230 and MR fluid residing therebetween.

FIGS. 7-9 show one preferred embodiment of the core side plate or disk216 of the prosthetic knee joint. 210. The core side plate 216preferably comprises a circular groove 260 to receive an O-ring 262(FIG. 1), lip seal or gasket and the like. This provides a dynamic sealbetween the rotatable side plate 216 and the inner surface of therotatable outer spline 232 and prevents leakage of MR fluid from theknee 210. The other side plate 218 is similarly configured to receive anO-ring 262 (FIG. 1) and provide a dynamic seal. In an alternativepreferred embodiment, two grooves or flanges are provided on the innersurface of the outer spline 232 to receive O-rings or the like andprovide a dynamic seal between the core side plates 216, 218 and theouter spline 232.

The O-rings 262 are fabricated from a suitable rubber material or thelike such as Viton, Teflon and Neoprene among others. In one preferredembodiment, the O-rings 262 have an inner diameter of about 50 mm and awidth of about 1.5 mm. In other preferred embodiments, the dynamic sealscan be dimensioned and/or configured in alternate manners with efficacy,as required or desired, giving due consideration to the goals ofproviding reliable seals, and/or of achieving one or more of thebenefits and advantages as taught or suggested herein.

The inner surface of the core side plate 216 preferably has a generallycircular shoulder or step 264 for aligning or locating with the innerspline 222 (FIG. 1). The outer surface of the core plate 216 preferablyhas a generally ring-shaped shoulder or step 266 for aligning orlocating with the outer fork 236 (FIG. 1). Optionally, the step 266 mayinclude a cut 268 to allow clearance space for electrical wires orleads. Other holes around the central cavity 256 may be provided forpassage of electrical wires or leads. Preferably, the outer surface ofthe core side plate 216 includes a tapered portion 270. Thisadvantageously decreases weight, saves material and also providesclearance space to facilitate assembly.

The core side plate 216 is preferably fabricated form a material havinga high saturation flux density, a high magnetic permeability and lowcoercivity. Advantageously, this facilitates in the construction of anartificial knee or brake that is compact and light weight, and alsostrong. In one preferred embodiment, the core plate 216 comprises anintegral unit. In another preferred embodiment, the core plate 216 isformed of laminated sheets to advantageously reduce or minimize eddylosses.

Preferably, the core plate 216 comprises an iron-cobalt (FeCo) highmagnetic saturation alloy. In one preferred embodiment, the core plate216 comprises Vacoflux 50 as available from Vacuumschmelze of Hanau,Germany. In another preferred embodiment, the core plate 216 comprisesIron-Cobalt High Saturation Alloy (ASTM A-801 Type 1 Alloy). In yetanother preferred embodiment, the core plate 216 comprises Vacoflux 17as available from Vacuumschmelze of Hanau, Germany. In a furtherpreferred embodiment, the core plate 216 comprises Hiperco Alloy 50. Inother preferred embodiments, the core plate 216 can be efficaciouslyfabricated from alternate soft magnetic materials or the like, asrequired or desired, giving due consideration to the goals of providinga suitably compact, light weight and/or durable prosthetic knee joint,and/or of achieving one or more of the benefits and advantages as taughtor suggested herein.

In one preferred embodiment, the material comprising the core plate 216has a saturation flux density of about 2.2 Tesla. Such a high saturationflux density is desirable because it allows a compact and light weightdesign. For example, if a material having a lower saturation fluxdensity was utilized, the cross-sectional area of the return paththrough the core plate 216 in the direction of the applied magneticfield would have to be increased to achieve the same dynamic torquerange. In other preferred embodiments, the core side plate saturationflux density can be higher or lower, as needed or desired, giving dueconsideration to the goals of providing a suitably compact, light weightand/or durable prosthetic knee joint, and/or of achieving one or more ofthe benefits and advantages as taught or suggested herein.

Preferably, the core side plate 216 is formed by machining followed byheat treatment in a hydrogen atmosphere to achieve optimal magneticproperties. In other preferred embodiments, the core side plate 216 canbe efficaciously fabricated from other techniques, for example, casting,forging, molding, laminating, among others, as required or desired,giving due consideration to the goals of providing desired magneticproperties and a suitably compact, light weight and/or durableartificial knee, and/or of achieving one or more of the benefits andadvantages as taught or suggested herein.

FIG. 10 shows one preferred embodiment of the inner spline 222 of theprosthetic knee joint 210. The inner spline 222 is preferably generallycylindrical in shape and comprises a substantially central cylindricalcavity or through hole 276 for receiving the electromagnet or magneticcoil 214 (FIG. 1). Alternatively, other suitable shapes for the innerspline 222 and cavity 276 may be efficaciously utilized, as needed ordesired.

Preferably, the inner spline 222 comprises a plurality of approximatelyequally spaced longitudinal through holes 278 arranged in a generallycircular fashion to receive end-threaded rods or bolts and the like tosecure selected components of the prosthetic knee 210, such as the coreside plates 216, 218 and the inner spline 222. These holes 278 aregenerally aligned with corresponding holes 258 of the core side plates216, 218.

In one preferred embodiment, the inner spline 222 comprises five holes278. In another preferred embodiment, the inner spline 222 comprisesthree holes 278. Alternatively, fewer or more holes 278 arranged inother fashions may be provided, as needed or desired.

The inner spline 222 preferably comprises a circular groove 260 at eachend to receive respective O-rings 282 (FIG. 1) or gaskets and the like.This provides a static seal between the inner spline 222 and the sideplates 216, 218, since these components rotate together during kneerotation, and prevents leakage of MR fluid from the knee 210. In analternative preferred embodiment, a respective groove or flange isprovided on the inner surfaces of either or both plates 216, 218 toreceive O-rings or the like and provide a static seal.

The O-rings 282 are fabricated from a suitable rubber material or thelike such as Viton, Teflon and Neoprene among others. In one preferredembodiment, the O-rings 282 have an inner diameter of about 30.5 mm(1.201 inches) and a width of about 0.76 mm (0.030 inches). In otherpreferred embodiments, the static seals can be dimensioned and/orconfigured in alternate manners with efficacy, as required or desired,giving due consideration to the goals of providing reliable seals,and/or of achieving one or more of the benefits and advantages as taughtor suggested herein.

The outer surface of the inner spline 222 preferably has a plurality ofapproximately equally spaced longitudinal grooves 284 which are adaptedto engage corresponding teeth of the rotors 220. In one preferredembodiment, the grooves 284 are generally semi-circular in shape. Inanother preferred embodiment, the grooves 284 are generally rectangularor square shaped with rounded corners. In other preferred embodiments,the grooves 284 can be efficaciously shaped and/or configured inalternate manners, as required or desired, giving due consideration tothe goals of providing reliable load transmission from the rotors 220 tothe inner spline 222, and/or of achieving one or more of the benefitsand advantages as taught or suggested herein.

The inner spline 222 is preferably fabricated from titanium or atitanium alloy, and more preferably from 16A1-14V titanium alloy.Advantageously, the use of titanium or titanium alloys provides a nearzero magnetic permeability and a yet strong, hard surface with lowweight to engage the rotors and transmit torque from them. An additionalbenefit is that the high resistivity of the material (titanium ortitanium alloy) reduces energy losses due to induced eddy currents. Inother preferred embodiments, the inner spline 222 can be efficaciouslyfabricated from other metals, alloys, plastics, ceramics among others,as required or desired, giving due consideration to the goals ofproviding an inner spline 222 of near zero magnetic permeability, and asuitably compact, light weight and/or durable artificial knee, and/or ofachieving one or more of the benefits and advantages as taught orsuggested herein.

Preferably, the inner spline 222 is formed by machining. In otherpreferred embodiments, the inner spline 222 can be efficaciouslyfabricated from other techniques, for example, casting, forging,molding, among others, as required or desired, giving due considerationto the goals of providing a suitably compact, light weight and/ordurable artificial knee, and/or of achieving one or more of the benefitsand advantages as taught or suggested herein.

In one preferred embodiment, the prosthetic knee 210 comprises an anglesensing potentiometer 322 (FIG. 1). The potentiometer 322 is connectedto an arm 324 and a mounting plate 326. The mounting plate 326 isconnected to the fork 238 utilizing screws 328 or the like and spacers330. An end 332 of the arm 324 is mechanically connected to the angledouter surface 334 of the fork 238 utilizing suitable screws or the like.

In one preferred embodiment of the present invention, the prostheticknee 210 further comprises an extension assist to help straighten theleg by urging or biasing the leg to extension by applying a controlledtorque or force. Any one of a number of devices, such as a spring-loadedextension assist, as known in the art may be used in conjunction withthe present invention.

The mounting forks 236, 238 (FIG. 1) of the magnetorheologicallyactuated prosthetic knee 210 are preferably in mechanical communicationwith the bearings 226, 228 respectively and transfer rotary motion to apylon or artificial shin portion of the amputee. Threaded studs 306 orother suitable connectors or fasteners are used to facilitate connectionof the mounting forks 236, 238 to a pylon or artificial shin portion ofthe amputee.

Preferably, the mounting forks 236, 238 are fabricated from anodized7075-T6 aluminum alloy. In other preferred embodiments, the mountingforks 226, 238 can be efficaciously fabricated from other metals,alloys, plastics, ceramics among others, as required or desired, givingdue consideration to the goals of providing suitably strong, durable,light weight and/or substantially non-magnetic mounting forks 226, 238,and/or of achieving one or more of the benefits and advantages as taughtor suggested herein.

In one preferred embodiment, the mounting forks 236, 238 are formed bymachining. In other preferred embodiments, the mounting forks 236, 238can be efficaciously fabricated from other techniques, for example,casting, forging, molding, among others, as required or desired, givingdue consideration to the goals of providing a suitably compact, lightweight and/or durable artificial knee, and/or of achieving one or moreof the benefits and advantages as taught or suggested herein.

In one preferred embodiment, and as shown in FIG. 1, the prosthetic knee210 further comprises a flexion stop system or assembly comprising acushioned stop or restraint assembly or system 246. The flexion stopsystem controls the maximum allowable flexion angle by physicallylimiting the rotation between the outer side forks 236, 238 and theouter spline 232, and hence the rotation of the knee joint. The stopsystem 246 (FIG. 1) generally comprises a plurality of stops, bands orstrips 312, 314 and 316.

Desirably, operation of a prosthetic knee in shear mode in oneembodiment utilizes a MR fluid that is operable over a temperature rangefrom about 10 to about 115° F., but also including about 20, 30, 40, 50,60, 70, 80, 90, 100, and 110° F. Operability in one embodiment dependson viscosity, wherein the carrier fluid desirably has a viscosity at104° F. (40° C.) of about 10 to about 100 cSt, more preferably viscosityof about 30 to about 80 cSt, even more preferably viscosity of about 50to about 70 cSt, but also including about 10, 20, 25, 35, 40, 45, 55,60, 65, 75, 85, 90, and 95 cSt. The viscosity of preferred MR fluids incertain embodiments may be altered by one or more of the following:increasing or decreasing the particle loading, including an additive,changing the carrier oil, or mixing two or more carrier oils.

In one embodiment, an MR fluid is specifically designed for use in ashear mode device. For such a device, mechanically hard particles aredesired. The carrier fluid also desirably experiences a less dramaticviscosity change over temperature changes as compared to other fluids.This may be measured in terms of a viscosity indices (test method ASTMD-2270) with preferred carrier fluids having higher viscosity indices.In one embodiment, preferred carrier fluids have viscosity indicespreferably ranging from about 100 to about 340 based on kinematicviscosity at 104 and 212° F., from about 120 to about 320, from about140 to about 300, but also including 160, 180, 200, 220, 240, 255, 260,280, and ranges encompassing these amounts. One embodiment thataccomplishes this includes a carrier fluid comprising one or more PFPEoils. For example, a preferred PFPE fluid, UNIFLOR™ 8510 has a viscosityindex of 255. Without wishing to be bound by any theory, it is believedthat preferred PFPE oils of certain embodiments demonstrate desirableviscosity indices due to their narrow distribution of molecular weights.Also, the MR fluid desirably does not produce a significant amount ofvapor in a sealed chamber so as to interfere with the function of thedevice. In one embodiment, a fluid component comprising PFPE oil carrierfluid and a fluoropolymer additive provides this property. Withoutwishing to be bound by any theory, it is believed that preferred PFPEoils of certain embodiments are less volatile, i.e. lower vaporpressures than other oils, because they have much higher molecularweights, e.g. about 2,000 to about 15,000, and therefore do not producea significant amount of vapor.

Desirably, operation of a prosthetic knee in shear mode in oneembodiment preferably utilizes a carrier fluid with a pour point (testmethod ASTM D-97) preferably ranging from about −70° C. to about −40°C., from about −65° C. to about −45° C., but also including about −50°C., −55° C., −60° C., and ranges encompassing these temperatures. ASTMD-97 method defines “pour point” as the lowest temperature at whichmovement of an oil is observed. In another embodiment, operation of aprosthetic knee in shear mode preferably utilizes a carrier fluid with apercent volatility at 121° C. (test method ASTM D-972) preferablyranging from about 0.01% to about 20%, from about 0.02% to about 15%,from about 0.03% to about 12%, but also including about 0.05%, 0.08%,0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.7%, 0.9%, 1%, 3%, 5%, 7%, 9%, 17%, andranges encompassing these percentages.

More specifically, when used in combination with a prosthetic knee aspreviously disclosed, desirable MR fluids for use in certain embodimentscomprise a carrier fluid and polarizable particles. More specifically,in one embodiment used in combination with a prosthetic knee, the MRfluid comprises one or more PFPE oil carrier fluids and polarizableparticles. In one embodiment, the iron particles comprise from about 1to about 60% (v/v) of the total MR fluid volume, preferably from about10 to about 50% (v/v), more preferably from about 20 to about 40% (v/v),but also including about 5, 15, 25, 30, 35, 45, and 55% (v/v), andranges encompassing these percentages.

In another embodiment, the MR fluid used in combination with aprosthetic knee may optionally comprise an additive. Suitable additivesinclude, but are not limited to, functionalized carrier fluids as wellas fluoropolymers. In one embodiment, the iron particles comprise fromabout 1 to about 60% (v/v) of the total MR fluid volume, preferably fromabout 10 to about 50% (v/v), more preferably from about 20 to about 40%(v/v), but also including about 5, 15, 25, 30, 35, 45, and 55% (v/v),and ranges encompassing these amounts. In one embodiment, the additivecomprises from about 0.1 to about 20% (v/v) of the carrier fluid,preferably from about 1 to about 15% (v/v), more preferably from about 2to about 10% (v/v), but also including 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6,6.5, 7, 7.5, 8, 8.5, 9, 9.5, 11, 12, 13, 14, 16, 17, 18, and 19% (v/v).For example, in one embodiment a preferred MR fluid used in combinationwith a prosthetic knee in shear mode comprises about 32% (v/v) particlesand about 68% (v/v) fluid component wherein said fluid componentcomprises about 5% (v/v) a parafluoropropene and oxygen polymerizedamide derivative additive and about 95% (v/v) perfluorinated polyethercarrier fluid. In another embodiment a preferred MR fluid used incombination with a prosthetic knee in shear mode comprises about 28%(v/v) particles and about 72% (v/v) fluid component wherein said fluidcomponent comprises about 5% (v/v) a parafluoropropene and oxygenpolymerized amide derivative additive and about 95% (v/v) perfluorinatedpolyether carrier fluid. In another embodiment, a preferred MR fluidused in combination with a prosthetic knee in shear mode comprises about32% (v/v) particles, and about 68% (v/v) fluid component wherein saidfluid component comprises about 5% (v/v) poly(hexafluoropropyleneepoxide) with a carboxylic acid located on the terminal fluoromethylenegroup additive and about 95% (v/v) PFPE oil carrier fluid. In anotherembodiment, a preferred MR fluid used in combination with a prostheticknee in shear mode comprises about 28% (v/v) particles, and about 72%(v/v) fluid component wherein said fluid component comprises about 5%(v/v) poly(hexafluoropropylene epoxide) with a carboxylic acid locatedon the terminal fluoromethylene group additive and about 95% (v/v) PFPEoil carrier fluid. In embodiments containing PFPE oil, the PFPE oil maycomprise substantially all one PFPE oil or a mixture of one or more PFPEoils.

The ingredients may be combined in any order and mixed by any suitablemeans including, but not limited to, stirring, agitation, blending orsonification. In accordance with a preferred embodiment, the MR fluid isprepared as described above. Prior to loading into the prosthetic knee,the MR fluid is stirred under vacuum using a high speed stirrer toremove any dissolved gases. In a preferred embodiment, the MR fluid isheated to about 90 to about 160° F., more preferably to about 100 toabout 150° F., even more preferably to about 110 to about 130° F., butalso including about 95, 105, 115, 120, 122, 125, 135, 140, 145, and155° F., under vacuum prior to loading into the prosthetic knee.

In another preferred embodiment, the MR fluid is heated at ambientpressure prior to being placed under vacuum. While under vacuum,agitation or stirring of the MR fluid is preferred but not required.After the MR fluid is released from the vacuum, the MR fluid is loadedinto the prosthetic knee. The loading of the prosthetic knee involvesadding the MR fluid to the knee and then placing the knee under vacuum.While under vacuum the knee is optionally agitated. To reduce the vacuumpressure, an inert gas is added into the vacuum chamber. Once, thevacuum is fully released, the prosthetic knee is removed and closed. Thevacuum fill process should be carefully monitored as exiting air mayblow enough MR fluid out of the funnel to require fluid volumereplenishment.

EXAMPLES Example 1 MR Fluid Preparation

To prepare the MR fluid, the additives were mixed with the carrierfluids and stirred. Carrier fluid was added to the iron particles andthe ingredients were stirred. A Branson Digital Sonifier, Model 450, wasused to disperse the iron particles in the carrier fluid. The MR fluidwas then placed on the sonifier table, with the probe adjusted so thatthe majority of the probe was immersed in the MR fluid without touchingthe bottom of the mixture jar. The MR fluid was then sonicated for 1.5minutes at 50% intensity while the sonifier table rotated. The MR fluidwas checked periodically to ensure that the mixture did not become toohot. A fan was used to cool the MR fluid. Once the cycle was complete,the jar was rotated to wash down any particles that were adhered to thewalls of the jar. The sonification step was then repeated two moretimes. Once complete, the MR fluid was removed from the sonifier and afinal stir of the MR Fluid was performed to ensure that there were noclumps in the MR fluid. The MR fluid was then placed in an oven for twohours at 50° C. (122° F.).

Example 2 Prosthetic Knee MR Fluid Loading

After the MR fluid was prepared, it was stirred to break up any smallagglomerates. The MR fluid was then placed under the vacuum chamberstirrer and the bell jar was placed over the fluid and stirrer. Thestirrer was turned on and vacuum was applied at 29.4″ Hg for 30 minutesto extract residual air. The fluid was stirred until no bubblesappeared. The stirrer and vacuum were then turned off and the pressurewas slowly increased. The container was then removed from the vacuumchamber.

A measured volume of MR fluid was then transferred into a funnelinserted into the prosthetic knee actuator. The knee was placed in thevacuum chamber and the chamber was sealed with a bell jar. Vacuum wasslowly drawn to 28″ Hg. The knee was periodically agitated during thisprocedure.

The vacuum chamber was slowly filled with nitrogen gas to remove thevacuum. Vacuum was slowly released at about 2″ Hg per 10 seconds. Theknee was agitated to help force the fluid into the knee. Nitrogen wasdisconnected from the vacuum chamber when the gage read zero. The vacuumchamber was then unsealed and the knee was removed. The funnel was thenremoved from the knee. Care was taken so as to avoid tipping the kneeduring this process, which would have resulted in a release of thenitrogen head. The knee was closed by inserting the appropriate setscrew with a torque of about 2.5 Nm applied to the screw.

Example 3 MR Fluid Settling Tests

Settling tests were conducted for thirteen different MR fluids. The rateof settling varied significantly and was found to be a function of ironparticle size, the use of additives, and the viscosity of the fluids.

Procedure for Settling Tests

MR fluids were formulated by adding carrier oil, with or without anadditive, to a jar containing a weighed aliquot of carbonyl ironparticles. For formulations containing an additive, the additive wasblended with the carrier oil prior to mixing with the iron particles.The components were mixed by hand for several minutes and then the ironparticles were dispersed using high frequency ultrasonic energy suppliedby a Branson Digital Sonifier, Model 450. The fluids were subjected to2-3 cycles of ultrasonic energy, each cycle having a duration of 1.5minutes and power amplitude of approximately 50%. The fluids were thenmixed again by hand to insure complete dispersion of the iron particles.Fluids were not degassed prior to starting the settling tests.

Approximately 8 mL of each of the well-mixed MR fluids were transferredto 10 mL graduated cylinders. The cylinders were closed by placing aground glass stopper into the neck of each cylinder.

The initial volume of MR fluid was recorded and the volume of settledmaterial was read and recorded at regular intervals for a period oftwenty-one days. The fraction of settling was defined as the volume ofcarrier oil, which separated from the MR fluid and floated on the top ofthe MR fluid divided by the initial fluid volume. TABLE 1 MR FluidsTested Dupont 157 FSL Particle Fluid Additive Loading Component (% (v/v)BASF (% (v/v) of (% (v/v) of Carrier Fluid of total Particle total MRtotal MR (% (v/v) of total fluid MR Fluid Type fluid) fluid) Fluidcomponent component) HQ81FS-28 HQ 28% 72% 95% Nye 8130 5% HQ85FSL-28 HQ28% 72% 95% Nye 8510 5% HS67FS5-32 HS 32% 68% 63.7% Nye 8510; 5% 31.3%Dupont GPL-103 HS8510FSL-25 HS 25% 75% 95% Nye 8510 5% HS8410FSL-28H HS28% 72% 95% Nye 8510 5% HS85FS10-28 HS 28% 72% 90% Nye 8510 10%HS85FS10-32 HS 32% 68% 90% Nye 8510 10% HS85FS1-32 HS 32% 68% 99% Nye8510 1% HS85FS5-32 HS 32% 68% 95% Nye 8510 5% OM8510-25 OM 25% 75% 100%Nye 8510 None OM85-25-1 OM 25% 75% 99% Nye 8510 1% OMPF-25 OM 25% 75%100% Nye 8130 None OMPFA-25 OM 25% 75% 95% Nye 8130 5%HQ Particle Size Ranges from about 0.5-2.0μHS Particle Size Ranges from about 1.5-3.5μOM Particle Size Ranges from about 2-9μ

Results

In general the largest iron particles, OM grade, settled the fastest,especially when the viscosity of the fluid was reduced by including theDupont 157 FSL additive in the formulation. However, the settling curvesfor the larger OM grade particles were initially steep and then leveledoff after 10 to 14 days. Settling rates for the smaller iron particles,HS and HQ grade, were nearly linear over the twenty-one day test period.

Overall, MR fluids with lower settling rates demonstrated longer lifeand greater durability during subsequent bench testing in prostheticknees. MR fluids with high settling rates produced hard caked settlediron particles. These fluids performed poorly in subsequent benchtesting in prosthetic knees. MR fluids with low settling rates producesoft settled iron particles. These fluids generally performed well insubsequent prosthetic knee bench tests.

Example 4 Viscosity and Shear Rate Testing

Dynamic viscosity of three mixed carrier oils and six MR fluids madefrom the mixed carrier oils were measured as a function of shear rate.Viscosity measurements were performed at ambient temperature (22° C.)using a Rheometric Scientific (TA Instruments) RFS-II rheometer with aparallel plate sample cell. All samples were run in duplicate withapproximately 1 cc of sample. Five of the samples were rerun induplicate on a second day due to incomplete mixing of the first samples.

Samples of mixed carrier fluids as well as MR fluids containing mixedcarrier fluids were tested. The samples and viscosity measurements wereas follows: TABLE 2 Sample Fluid Component BASF HS particles Viscosity(cP) Name %((v/v)) %((v/v)) at 100 s⁻¹ A 100¹ 0% 115 B 100² 0% 121 C100³ 0% 145 A-32 68¹ 32% 681 A-40 60¹ 40% 1371 B-32 68² 32% 780 B-40 60²40% 1651 C-32 68³ 32% 917 C-40 60³ 40% 1725¹Fluid component consisting of 47.5% (v/v) Nye 8510 carrier fluid, 47.5%(v/v) Dupont GPL-103 carrier fluid; 5% (v/v) Dupont 157-FSL additive.²Fluid component consisting of 63.7% (v/v) Nye 8510 carrier fluid, 31.3%(v/v) Dupont GPL-103 carrier fluid; 5% (v/v) Dupont 157-FSL additive.³Fluid component consisting of 71.3% (v/v) Nye 8510 carrier fluid, 23.7%(v/v) Dupont GPL-103 carrier fluid; 5% (v/v) Dupont 157-FSL additive.

The dynamic viscosity curves which were measured at ambient temperature(22° C.), for the samples above are illustrated in FIGS. 3, 4, and 5.FIG. 3 represents the viscosity, η, versus shear rate curves for thethree mixed carrier oils, A-C, and a sample of 100% ((v/v)) Nye 8510oil. All of the mixed carrier oils had a lower viscosity than Nye 8510.The typical viscosity specification value for Nye 8510 oil is 65 cSt at40° C., while the Dupont GPL-103 oil had a viscosity of 30 cSt at 40° C.

FIG. 4 represents the viscosity, η, versus shear rate curves for thethree mixed carrier oil MR fluids containing 32% ((v/v)) of HS ironparticles and a MR fluid which contains 100% Nye 8510 carrier oil and32% ((v/v)) of HS iron. Viscosities of the mixed carrier oil MR fluidswere less than the MR fluid containing only Nye 8510. This datademonstrated that it was possible to reduce the viscosity of a MR fluidby decreasing the viscosity of the carrier oil. Viscosity of the mixedcarrier oil MR fluids was lowered in proportion to the amount ofGPL-103, which was added to the carrier oil. The three mixed MR fluidsexhibited Non-Newtonian behavior as the viscosity of these fluidschanged continually with shear rate. The viscosity of these fluids wasapproximately six times that of the corresponding carrier oil at a shearrate of 100 s⁻¹.

FIG. 5 represents the viscosity, η, versus shear rate curves for thethree mixed carrier oil MR fluids which contain 40% ((v/v)) of HS ironparticles. The viscosities of these fluids were considerably larger thanthe viscosities of the MR fluids, which contained 32% ((v/v)) iron.Viscosity of the mixed carrier oil MR fluids containing 40% ((v/v)) ironwas lower for the fluids with higher amounts of GPL-103, however, theviscosity curve for B-40 was higher than expected. This apparent anomalywas mostly likely caused by incomplete mixing of the viscous 40% ((v/v))iron MR fluids prior to the viscosity measurements. The three MR fluidsexhibited Non-Newtonian behavior as the viscosity of these fluidschanged continually with shear rate. The viscosity of these fluids wasapproximately twelve times that of the corresponding carrier oil at ashear rate of 100 s⁻¹.

FIG. 6 summarizes the comparison of the viscosities of the three mixedcarrier oils to Nye 8510 and the viscosities of the six mixed carrieroil MR fluids to that of a MR fluid containing only Nye 8510. Nye 8510had a viscosity of 240 cP at 100 s⁻¹, while the three mixed carrier oilswere well below 200 cP. The MR fluid which contained only Nye 8510 and32% ((v/v)) iron, namely HS8510FS5-32, has a viscosity of 1,100 cP at100 s⁻¹, while the MR fluids containing mixed carrier oils and 32%((v/v)) iron had viscosities of 680, 780 and 917 cP at 100 s⁻¹respectively, for the fluids which contain 50, 67 and 75% ((v/v)) of Nye8510. Viscosity of the MR fluids containing 32% ((v/v)) iron increasedwith increasing amounts of the more viscous Nye 8510. Viscosity of theMR fluids containing 40% ((v/v)) iron also increased with increasingamounts of Nye 8510.

Results indicated that the three carrier oils exhibited near Newtonianbehavior, while the six MR fluids all exhibited Non-Newtonian behavior.Viscosity of the MR fluids were shown to be a function of both ironloading and carrier oil viscosity. For MR fluids with 32% ((v/v)) ironloading the viscosity was approximately six times that of thecorresponding carrier fluid. For MR fluids with 40% ((v/v)) iron loadingthe viscosity was about twelve times that of the corresponding carrierfluid. All of the MR fluids exhibited thinning i.e. a reduction inviscosity as a function of shear rate, especially at low shear rates.

Example 5 Prosthetic Knee Testing

Numerous prosthetics knees operating in shear mode were filled withvarious MR fluids and tested for fluid performance, low-end torque,cavity pressure, and overall durability of the knee. Testing wasperformed to simulate use of the knee by an amputee. The knees weretested using a custom made test bench in conjunction with LabVIEW dataacquisition software (National Instruments). The test machine rotatedthe prosthetic knees at a rate of 32,000 cycles per day in order tosimulate accelerated knee usage. Prosthetic knees of varyingconfigurations were used with numerous MR fluid compositions. The goalwas to achieve three million cycles without knee failure. Due to limitedequipment, testing of several knees was cut short in order to test otherfluids and/or knee configurations. The following table illustrates someof the testing. TABLE 3 Fluid Name Fluid Composition* Fluid PerformanceDuration of Test OMPF-25 75% fluid component¹; Unit ran smoothly, offstate torque 2.2 million cycles 25% BASF OM at end of test was 0.7 N-m.particles. Applied field torque at end was 49 N-m. HS8510FSL-28 72%fluid component²; Unit ran well, off state torque at 1.2 million cycles28% BASF HS end of test was 0.8 N-m. Applied particles. field torque atend was 33 N-m. HQ8510FSL-28 72% fluid component²; Unit ran well, offstate torque at 2.4 million cycles 28% BASF HQ 2.2 million cycles was0.8 N-m. particles. Applied field torque at 2.2 million cycles was 43N-m. HS8510FSL-25 75% fluid component²; Unit ran well, off state torqueat 862,000 cycles 25% BASF HS 800,000 cycles was 0.6 N-m. particles.Applied field torque at 800,000 cycles was 40 N-m. HS67FSL-32 68% fluidcomponent³; Two units, A1 and A2, produce A1—433K cycles. 32% BASF HSimproved initial applied field A2—290K cycles. particles. torque 47-50N-m. Initial off state torque was in the range of 0.6- 0.8 N-m. A1 at433K was at 44 N-m. A2 at 290K was at 47 N-m.*All percentages are % (v/v).¹Fluid component consisting of 100% Nye 8130 carrier fluid.²Fluid component consisting of 95% Nye 8510 carrier fluid and 5% Dupont157-FSL additive.³Fluid component consisting of 63.7% Nye 8510 carrier fluid, 31.3%Dupont GPL-103 carrier fluid, and 5% Dupont 157-FSL additive.

The various methods and techniques described above provide a number ofways to carry out the invention. Of course, it is to be understood thatnot necessarily all objectives or advantages described may be achievedin accordance with any particular embodiment described herein. Thus, forexample, those skilled in the art will recognize that the compositionmay be made and the methods may be performed in a manner that achievesor optimizes one advantage or group of advantages as taught hereinwithout necessarily achieving other objectives or advantages as may betaught or suggested herein.

Furthermore, the skilled artisan will recognize the interchangeabilityof various features from different embodiments. Similarly, the variousfeatures and steps discussed above, as well as other known equivalentsfor each such feature or step, can be mixed and matched by one ofordinary skill in this art to perform methods in accordance withprinciples described herein.

Although the invention has been disclosed in the context of certainembodiments and examples, it will be understood by those skilled in theart that the invention extends beyond the specifically disclosedembodiments to other alternative embodiments and/or uses and obviousmodifications and equivalents thereof. Accordingly, the invention is notintended to be limited by the specific disclosures of preferredembodiments herein, but instead by reference to claims attached hereto.

1. A magnetorheological fluid comprising polarizable particles and afluid component, wherein the fluid component comprises a carrier fluidand an additive; wherein the additive comprises a functionalizedperfluorinated polyether fluid.
 2. The magnetorheological fluid of claim1, wherein the functionalized perfluorinated polyether fluid comprises amonofunctionalized perfluorinated polyether fluid.
 3. Themagnetorheological fluid of claim 2, wherein the monofunctionalizedperfluorinated polyether fluid comprises a functional group selectedfrom the group consisting of silane, phosphate, hydroxyl, carboxylicacid, alcohol, and amine.
 4. The magnetorheological fluid of claim 1,wherein the functionalized perfluorinated polyether fluid comprises adifunctionalized perfluorinated polyether fluid.
 5. Themagnetorheological fluid of claim 4, wherein the difunctionalizedperfluorinated polyether fluid comprises a functional group selectedfrom the group consisting of dihydroxyl, ethoxy ether, isocyanate,aromatic, ester, and alcohol.
 6. The magnetorheological fluid of claim1, wherein the polarizable particles comprise iron particles.
 7. Themagnetorheological fluid of claim 1 wherein the polarizable particlesrange in size from about 0.2 to about 50 microns.
 8. Themagnetorheological fluid of claim 7 wherein the polarizable particlesrange in size from about 0.4 to about 10 microns.
 9. Themagnetorheological fluid of claim 8 wherein the polarizable particlesrange in size from about 0.5 to about 9 microns.
 10. Themagnetorheological fluid of claim 1 wherein the polarizable particlescomprise about 1 to about 60% (v/v) of the total magnetorheologicalfluid volume.
 11. The magnetorheological fluid of claim 10 wherein thepolarizable particles comprise about 10 to about 50% (v/v) of the totalmagnetorheological fluid volume.
 12. The magnetorheological fluid ofclaim 11 wherein the polarizable particles comprise about 20 to about40% (v/v) of the total magnetorheological fluid volume.
 13. Themagnetorheological fluid of claim 1 wherein the carrier fluid isselected from the group consisting of silicone, hydrocarbon, esters,ethers, fluorinated esters, fluorinated ethers, mineral oil, unsaturatedhydrocarbons, and combinations thereof.
 14. The magnetorheological fluidof claim 1 wherein the additive comprises from about 0.1 to about 20%(v/v) of the fluid component.
 15. The magnetorheological fluid of claim14 wherein the additive comprises from about 1 to about 15% (v/v) of thefluid component.
 16. The magnetorheological fluid of claim 15 whereinthe additive comprises from about 2 to about 10% (v/v) of the fluidcomponent.
 17. The magnetorheological fluid of claim 1 comprising: about28% (v/v) polarizable particles; and about 72% (v/v) fluid component;wherein said fluid component comprises about 5% (v/v) additive and about95% (v/v) perfluorinated polyether carrier fluid.
 18. Themagnetorheological fluid of claim 1, wherein the functionalizedperfluorinated polyether fluid comprises a poly(hexafluoropropyleneepoxide) with a carboxylic acid located on the terminal fluoromethylenegroup.
 19. A magnetorheological fluid comprising polarizable particlesand a fluid component, wherein the fluid component comprises a carrierfluid and an additive; wherein the additive comprises a functionalizedfluoropolymer.
 20. The magnetorheological fluid of claim 19, wherein thefunctionalized fluoropolymer comprises a parafluoropropene and oxygenpolymerized amide derivative.